This PDF file contains the front matter associated with SPIE Proceedings Volume 11912, including the Title Page, Copyright information, and Table of Contents.

The fused silica is an important optical material in the large laser devices, which are often subject to laser induced damage in the laser systems. In this work we studied nanosecond laser induced damage in JGS1 fused silica at the three harmonic wavelengths of the 1064 nm, 355 nm and 248 nm. Under 1064nm/10ns, 355nm/10ns and 248nm/22.8ns laser irradiation, the bulk damage threshold is 150 J/cm², 15 J/cm² and 7 J/cm², respectively. The results showed that the weakest point of bulk damage threshold among the three tested wavelengths is 248 nm. And the damage threshold decreases sharply with the decrease of wavelength.

In this paper, the damage characteristics of MgF₂ window material were investigated by building a 193 nm UV excimer laser damage experimental system under different laser fluences of 193 nm excimer laser. The damage morphology was also observed by differential phase contrast microscopy (DIC). The damage mechanism of 193 nm excimer laser irradiated MgF₂ window material was investigated. Finite element simulation experiments were also conducted for the defective MgF₂ window material. The distribution of temperature and stress fields in the 193 nm UV laser irradiated MgF₂ window material was numerically analyzed using the finite element method. The results show that when the laser irradiates the MgF₂ window material, the damage threshold of the rear surface of the window material is 2.523 J/cm² and the damage threshold of the incident surface is 9.74 J/cm², that is, the rear surface is damaged before the incident surface. At the same time, the rear surface damage profile increased catastrophically with the growth of irradiated laser energy, while the incident surface damage profile increased linearly with the growth of irradiated laser energy. The main factor causing the damage to the window material is the damage caused by the defects contained in it, which causes stress damage to the window material during laser irradiation.

Visible laser of Pr³⁺ ions doped in fluoride glass fibers has found numerous applications in display techniques, visible light communication and scientific research. Unfortunately, the poor mechanical strength, degraded chemical stability and high cost limit the further development of fluoride glasses in practice. Instead, oxide glass is good host candidate for fiber lasers due to its advantages of mature processing technique, stable chemical properties, high mechanical strength and low cost. But it is difficult to achieve laser output at visible wavelengths in Pr³⁺ doped oxide glass fiber because of photodarkening after exposure to 488 nm laser. In this work, we study such photodarkening effect and relevant mechanisms in Pr³⁺ doped silicate glasses and fibers by using X-ray and 488 nm laser as irradiation sources, respectively. Results indicate that due to relatively low energy of Pr³⁺: 4f5d, electrons of Pr³⁺ ions will be trapped to form defect (trapped hole center) through excited state absorption under exposure to both 488 nm laser and X-ray radiation.

Lightweight optics utilized in high-power laser system can dissipate heat better and reduce system weight. Dielectric films can be designed for laser pulse modulation, high reflect rate and wide bandwidth. However, the deformation caused by coating residual stress will be large due to the large thickness of dielectric films and low stiffness of lightweight mirror, which brings a large bending deformation with the temperature variation. The traditional surface compensation technology is double-sided coating, but it is not suitable for lightweight mirrors. In this study, we construct a finite shell-element model to estimate the surface shape error caused by dielectric film coating residual stress on a lightweight mirror for surface pre-processing. Thermal deformation and bimetal effect deformation are also simulated.

The fused silica play a key role among the High laser power device as the laser-transmitter. Many factor induced the damaging, such as the surface topography, the defect (bubbles, particulates), the doped-elements which can absorbing the laser-energy. Among them, the absorption of the specific wavelength laser can lead to the heating up which provide the motive power for the Silica tetrahedron Lattice disintegration. We did research on the absorption of the specific wavelength laser to find the relationship among the manufacturing process, the structure of the fused silica and the Laser damage threshold. From the research, there is rarely any relationship between the extent of the absorption of the specific wavelength laser and the OH. While the purity is the key factor.Although the Impure substance will lead to weak absorption, the LIDT of the 1064nm is beyond 100J/cm².

HfO₂ thin films are widely used in laser system because of its superior optical and mechanical properties, especially high laser induced damage threshold. In this paper, single-layer HfO₂ thin films were prepared by APS plasma assisted electron beam evaporation deposition. The effects of oxygen charging of electron gun, baking temperature, discharge current of APS source and bias voltage of APS source on optical properties, surface roughness, standing wave electric filed and laser induced damage threshold of HfO₂ thin films were studied by orthogonal experiment. Experiment and analysis results showed that the characteristics of HfO₂ thin films are closely related to the oxygen charging of electron gun, baking temperature and APS assisted processing parameters. Especially, baking temperature, oxygen charging of electron gun and bias voltage of APS source have great influence on laser induced damage threshold. Through the analysis of experimental date, the optimal combination of process parameters for APS assisted electron beam evaporation of HfO₂ optical films were obtained.

The fused silica optics are important functional ultraviolet optical elements in the high-power laser system. Contamination plays an extremely important role in laser-induced damage, which will affect the laser damage threshold of the components to varying degrees, and finally affects the output flux of high-power laser system. An organic solvent needs to be used to wipe the optical surface before applying it, and this process will introduce organic pollution. In addition, different optical films and organic solvents have different effects on the laser damage threshold of fused silica, which need to be studied further. In this work, the photo-thermal weak absorption platform was used to test the photothermal weak absorption of three samples before and after the organic solvent treatment. The first sample was tested on the surface of the fused silica substrate; the surface of the second sample was coated with aluminum oxide; and the surface of the third sample was coated with hafnium oxide. The results show that the use of ethanol can increase the photo-thermal weak absorption of the substrate by 29.6%; the photo-thermal weak absorption signal of the fused silica element coated with aluminum oxide is reduced by 20% after the surface is wiped with ethanol; the fused silica element with hafnium oxide coated on the surface reduces the photo-thermal weak absorption signal by 33%. The experimental results verify the feasibility of using ethanol to wipe fused silica components.

In large high-power laser devices,the surface and subsurface defects of fused silica optical components directly affect the laser damage threshold and imaging quality. In this paper, fluorescence imaging technology is used to obtain images of defects in the subsurface layer of optical components that will absorb laser. Because the original image has the characteristics of sparse signal, weak intensity, low contrast, etc. In order to efficiently and reliably evaluate the surface and subsurface defects, this paper proposes a weak and small defect detection method based on local adaptive contrast enhancement and seed region growth. Firstly, the local adaptive contrast enhancement method is used to enhance the contrast of the original image. Secondly, the method of bilateral filtering is used to denoise. Thirdly, seed region growth method is used to segment the defective regions and perform morphological processing. Finally, defect detection is performed. The experiment uses different segmentation methods to detect images in different regions. The results show that this method can significantly enhance the contrast of the original fluorescence image, and detect pixel-level defects, and the detection rate is stable at about 95%. Meanwhile, the reasons, size distribution and other characteristics of the sub-surface defects of fused silica optical components are analyzed. This paper provides a nondestructive method of detecting weak and small defects in the subsurface layer of the optical element faster and higher accuracy.

The study of the influence of the changes of laser parameters on the temperature field distribution of PbS detector irradiated under 2.79μm mid-infrared laser has important reference value. In this paper, the theoretical simulation of a typical PbS detector irradiated by a 2.79μm mid-infrared laser is carried out by using the Finite Element Analysis method (FEA). The maximum temperature of PbS detector irradiated by 2.79μm mid-infrared laser with different laser parameters is investigated. The maximum temperature on the photosensitive surface of the PbS detector under different conditions is obtained by adjusting the spot radius, pulse width, and repetition frequency of the simulated pulsed laser. The effects of the changes of spot size, repetition frequency and pulse width on the maximum temperature of the photosensitive surface are investigated. The simulation results show that under the same energy density irradiation condition, the maximum temperature of the photosensitive surface decreases with the increase of the spot radius and pulse width. Under the condition of the same spot radius and pulse width, the higher repetition frequency can make the maximum temperature of photosensitive surface reach a higher temperature. This work gives the law of the temperature changes of the photosensitive surface caused by changing the laser parameters, which is helpful to improve the damage resistance of PbS detector to high power 2.79μm mid-infrared laser step by step.

The deep ultraviolet optical thin films play an important role in excimer lasers, deep ultraviolet lithography machine and other laser systems. In this paper, the experiment on damage in HfO₂/ SiO₂ high reflective film irradiated by 248nm ultraviolet excimer laser was carried out. And the high reflection film is coated with a layer of SiO₂ as a protective film. The damage morphology and depth of the samples were observed and analyzed by means of DIC microscope and surface profiler system. In this experiment, the laser-induced damage threshold of HfO₂/ SiO₂ high reflective film coated with SiO₂ protective film was calculated by zero damage probability. Based on the surface characteristics of the damage points, we established the model to analyze the damage mechanism of the high reflectance film by using Finite Element Method(FEM). The experimental results show that the damage threshold of 248nm excimer laser to the highly reflective film is 3.086J/cm². When the incident laser energy is 3.33J/cm², stress damage appears on the surface of the highly reflective film. With the increase of laser energy, the high reflective film will appear melting damage and corrugated damage.

The uncertainty of the space radiation environment model has an impact on the evaluation of the solar absorption rate of spacecraft thermal control materials in the space radiation environment. This paper uses the space integrated radiation ground simulation test device to experimentally study the solar absorption rate change law of the ITO/Kapton/Al thermal control film under the electron and proton irradiation environment, and then the uncertainty of the space radiation environment model is compared to the ITO/Kapton /Al thermal control film to analyze the influence of solar absorptivity. The research shows that with the increase of the radiation fluence, the influence of different uncertainties on the solar absorption of the thermal control film first increases and then decreases, and the final effect is basically negligible; the uncertainty on the solar absorption of the thermal control film material When the uncertainty factor increases, when the uncertainty factor is less than 1, the relative deviation caused by the uncertainty of the space radiation environment model to the solar absorption rate evaluation of the thermal control film is positive, when the uncertainty factor When it is greater than 1, it is negative.

Silicon rubber and gray cable commonly used on spacecraft was selected as contamination sources, quartz crystal microbalance (QCM) was used as a monitoring device for molecular contamination deposition, and quartz glass was used as a collection plate for molecular contamination. The influence of different temperatures such as 100°C, 125°C, 150°C on the outgas contamination of silicone rubber and gray cable research was carried out in a vacuum environment , and the influence of different deposition temperature such as 10°C, 25°C, 40°C, 55°C, 70°C on the amount of contamination deposition was studied too. The spectral properties and morphology changes of quartz glass at a heating temperature of 125°C on the contamination sources and a deposition temperature of 25°C were studied. The research results show that as the deposition time increases, the amount of contamination deposits approximately linearly increases. With the increase of space temperature, the amount of outgas contamination deposits increases significantly, and as the temperature of the deposition surface increases, the contamination deposits exponentially decreases. The contamination deposits on the surface of quartz glass are in the form of droplets, and the droplets are of different sizes and randomly distributed. After being contaminated by molecular contamination, the optical transmittance of quartz glass significantly decreases.

Polyimide film can be used in spacecraft thermal control multilayer and large-scale deployment structure, and its mechanical properties will be degraded by the influence of space radiation environment such as electron and proton. In this paper, the mechanical properties of polyimide film under the synergistic effect of electron and proton was studied using the space integrated irradiation test facility in Beijing Institute of Spacecraft Environment Engineering. It is found that the combined irradiation of electron and proton damages the polyimide film more than the single environment of electron or proton. The synergistic effect of electron and proton causes the exponentially decrease of rupture elongation and the tensile strength of the polyimide film with. With the increase of the electron and proton irradiation fluence until its properties reaches a steady state.

The shape and value of optical non-uniformity are of great significance to optical materials and directly determine whether optical materials can process into finished components in optical systems. TiO₂– SiO₂ glass is usually used to prepare high-precision lightweight space mirrors and large-scale ground-based telescopes due to its low expansion. The corresponding relationship between the surface shape change and the temperature change of the glass prepared by CVD process needs to be verified. The shape of the silica glass with different doping contents is manufactured to 50×8 mm, and the surface shape of samples is polished to about 0.5λ (λ=632.8 nm). A ZYGO laser plane interferometer with a 100 mm aperture is used to test the samples' optical non-uniformity values and optical stability under the rapid change of temperature. The results show that the doping of TiO₂ can significantly improve the optical stability of silica glass. When the sample is rapidly cooled from 80 to 20 , the change rate of PV value is only 0.01~0.02λ (λ=632.8nm). The morphology and numerical value (Δn=10ppm) of optical inhomogeneity can be used as optical transmission materials. Silica glass doped with 7.5-10wt% TiO₂ has good optical stability, and the transmittance of visible light and near-infrared light is greater than 90%. Its optical inhomogeneity is in the order of 10^-5, and its morphology has no apparent mutation. Therefore, it can be used as a reflective material and as a transmissive material in optical systems.

The distortion caused by temperature change in optical materials seriously impacts the accuracy and stability of optical systems, and it is vital to develop a transmission and reflection optical material with ultra-high optical stability. Doping TiO2 in silica glass can greatly reduce the thermal expansion coefficient of silica glass, improve the thermal stability of silica glass, and improve its optical stability. We used SiCl4 and TiCl4 as precursors to prepare glass materials with different titanium contents by CVD process in this work. After the precursors are thoroughly mixed, they enter the high-temperature furnace with a hydrogen-oxygen flame for chemical reactions. The granular SiO₂ and TiO₂ mixture generated by the reaction is deposited on the bottom of the furnace under gravity and sintered layer by layer to form a transparent glass body. The spectral transmittance and structural characteristics of glasses with different titanium contents were characterized by Raman spectroscopy and ultraviolet-visible-near infrared spectrophotometer to analyze the spectral transmittance and microstructure characteristics of the materials. The test results show that silica glass doped with 7.5- 10wt% TiO₂ has good optical stability, and the transmittance of visible light and near-infrared light is greater than 90%. The doping of TiO₂ makes the silica glass network show a specific ‘deaggregation’ phenomenon, but the tetrahedral framework of the silica glass is maintained. In addition to the tetrahedral form of Ti ions in the silica glass network, there is also the six-coordinated octahedral form.

The dichroic mirror is broadly used in the broad-field multi-object spectrometer, which is the key component to separate incident light into several wavelength channels. The design and fabrication of the broad angular spectrum dichroic mirror is investigated in this paper. The global optimization is applied to obtain the low passband ripple and the sharp transition between the transmissive and reflective wavelength range. The dichroic mirror was prepared by ion beam sputtering deposition. The results showed the average reflectance was larger than 99% between 310nm and 550nm and the transmittance (single side, mean-polarization) was larger than 98% between 570nm and 1000nm with the angle of incidence 28°± 5°. The film thickness distribution and film sensitivity of the dichroic film were also analyzed. This research relieves the feasibility of the design and fabrication of the broad angular spectrum dichroic mirror by ion beam sputtering deposition process.

The volume Bragg grating (VBG) recorded in the photo-thermo-refractive (PTR) glass has high diffraction efficiency (DE), excellent angle selectivity, multiplexed and flexible design, which is an ideal device to achieve the angle magnification of beam scanning. In this study, a 4-channel multiplexed VBGs with the average relative diffraction efficiency (RDE) greater than 96% at 1064 nm and the maximum discrete angle deflection of 12° was designed and fabricated. And the angle deviation of experiments and design schemes were controlled less than 0.3°. The laser damage of PTR glass and multiplexed VBGs were also tested at 1064 nm. Laser damage tests were performed with a beam diameter of 0.3 mm by "1-on-1" mode. It showed that the laser damage threshold of PTR glass and multiplexed VBGs were 44.33J/cm² and 30.15 J/cm² respectively.

Monocrystalline silicon reflectors are widely used in infrared high energy laser systems. In order to ensure the system to achieve high precision and high stability of beam transmission, the reflector needs to have a good laser load capacity for high power density laser under long time irradiation. However, the evaluation of reflector laser load capacity is influenced by multiple factors, which is difficult to be decoupled one by one, and the multiple index systems are not perfect. In this paper, multi-modal characterization methods such as reflectivity, fluorescence detection and surface roughness detection are proposed to establish the influence model of multiple influencing factors on the laser load capacity of monocrystalline silicon reflector. Through quantitative analysis of these defects with specific types and different properties, the surface cleanliness and integrity of the monocrystalline silicon reflector were analyzed from different angles, and the influence trend of each influencing factor on the laser load capacity of the element was obtained. In this paper, a relatively completed characterization system of monocrystalline silicon and the influence model of the laser load capacity of the monocrystalline silicon reflector have been established effectively. The influencing factors of the laser load capacity on the surface of the monocrystalline silicon reflector are evaluated effectively, which lays a foundation for the efficient acquisition of the monocrystalline silicon reflector with high load capacity.

In this work, based on the double cylindrical wave holographic interference method, a broadband chirped volume Bragg grating (CVBG) in photo-thermo-refractive glass (PTR) has been fabricated and studied, which has a diffraction bandwidth of about 23.8 nm. The transmittance and diffraction efficiency (DE) of the prepared CVBG were measured. The results showed that the DE and refractive index modulation (RIM) of the CVBG samples increased first and then decreased with the increase of the heat treatment time. And the transmittance of all samples decreased, indicating that the losses (sum of absorption and scattering) of the samples increased. It was found that the absorption coefficients of all samples did not exceed 0.1cm-1 even after prolonged heating, and the scattering losses accounted for the main part losses of the CVBG. Then, the thermostatic duration of the sample was shorter during heat treatment at the first time, the starting point of the RIM of CVBG became higher, which is expected to obtain higher RIM and DE of the CVBG in the subsequent heat development process. Although increasing the dose of UV exposure can reduce the losses of the CVBG, it is not conducive to the improvement of the RIM and DE of the CVBG. Therefore, we have made restrictions on both the dose of UV exposure and the duration of heat treatment. Finally, based on the fundamental matrix (F-matrix) method, the influence of the key structural parameters of the CVBG on its diffraction characteristics was analyzed, and a guidance scheme for making high-efficiency CVBG was proposed.

Molecular contamination from organic materials can lead to the performance degradation of sensitive optical devices on the spacecraft. Space ultraviolet (UV) radiation may influence the contamination effect, but relative research is non-sufficient. In this paper, experimental research of UV radiation enhancement effect on molecular contamination of sensitive optical device is implemented. The experimental system is designed based on the ASTM E1559 standard, in which the outgassing stage or deposition stage is under UV radiation, and UV enhancement effect under different contamination source and heating and deposition temperature are obtained. It is discovered that UV radiation results in obvious enhancement effect on the outgassing and deposition stage. When the outgassing stage is radiated by UV, in the heating temperature between 100~150℃, the contamination mass of silicone rubber is increased by 158%~677%, and that of cable insulation is increased by 51%~86%. When the contamination deposition stage is radiated by UV and the deposition temperature is between 5~70℃, the deposition of silicone rubber is increased by 1.16~1.91times, and that of cable insulation is increased by 1.48~8.82 because of UV radiation. In addition, the transmissivity of glass specimens with and without UV radiation are tested, and the morphology of contaminants deposited on the glass specimens are observed, which also indicate that UV radiation leads to the deterioration of the contamination effect. The research reveals the enhancement effect of molecular contamination process by UV radiation quantitatively, which can provide better theoretical support for contamination control of sensitive optical devices on spacecrafts.

With the development of space lasers, research on the stability of laser films in space environments is becoming more and more important. The space laser film will be damaged by protons, gamma rays and other space radiation environments, and it will be affected by laser radiation, too. This puts forward higher requirements for space laser film elements, so it is essential to carry out space environment simulation tests on laser films. In this paper, the effect of 40keV proton on SiO₂ film was studied and then the 355nm laser damage threshold test on it was performed. It was found that the ultraviolet absorption of the film irradiated by proton increased, resulting in the decrease of its transmittance and its ability to resist laser damage.

Ni based nano/micro structures are wildly applied in fabrication of nano/micro imprint template, meta-surface, diffractive elements, etc. In this work, the fabrication of Ni structures by electroplating method on a AIST resist is studied. AIST is first deposited on glass substrate to form a layer of thin film. Then, the film is exposed to arbitrary pattern structure by laser direct writing system. And the exposed region changes from amorphous state to crystalline state due to photo-thermal physical reaction. Owing to the different development rates of the exposed region and the non-exposed region, the micro/nano structures can be obtained. Subsequently, continuous Ni structures were formed by electroplating method on the former AIST structure which confirmed by the images of optical microscope(OM) and scanning electron microscope(SEM). This work greatly broadens the application scope and prospect of direct laser writing in heat- mode lithography technology.

Multilayer dielectric gratings (MLDGs) have been widely used as pulse compression grating (PCG) in chirped pulse amplification (CPA) technology due to their high laser induced damage thresholds (LIDTs). The quest for MLDGs LIDTs improvement is endless. As one of the core components of CPA process, MLDGs will encounter laser irradiation of nanosecond, picosecond and femtosecond. Therefore, the damage characteristics of MLDGs should be studied at various pulse widths. We performed the LIDTs test on a Nd:YAG laser system with a wavelength of 1064 nm and a pulse width of 8 ns. Damage characteristics of both MLDFs and MLDGs were investigated. MLDFs were deposited on the substrates cleaned by hand wipe or ultrasonic cleaning. The results show that the LIDTs of MLDGs are approximately 60% of MLDFs. Besides, LIDTs of MLDFs with HfO₂ top layer will not be affected by the methods of substrates cleaning due to its surface damage characteristic related to the non-zero EFI on the surface material. However, for the MLDFs with top layer of Ta₂O₅, LIDTs of MLDFs deposited on substrates cleaned by hand wipe are higher than those deposited on the ultrasonically cleaned substrates.

The surface quality of the optical element substrate will affect the laser damage threshold of the dielectric coatings. Substrate surface scratches are one of the common damages to the substrate. In this work, the parabola-section-model lateral scratches of the 45° HR coating with a central wavelength of 1064 nm substrate are studied, and the scratches and multilayer coatings are established. The three-dimensional finite element method is used to simulate the electric field modulation generated by scratches in the fundamental frequency high-reflective film when coatings irradiated at 1064nm and 355nm . The results show that under the same conditions, greater light intensification at the shorter wavelength.The electric field enhancement of p-polarized light is larger than that of s-polarized light. For 1064nm laser, when the incident angle is 45° The electric field intensity is the highest. When the incident laser at 355nm , the maximum intensity enhancement is produced when the incident is 60à.When the laser is incident at 45°, the greater the depth of the scratch, the stronger the electric field intensity in the film. The angle at which the 355nm laser is irradiated on the surface of the recessed film determines the magnitude of the electric field enhancement. Therefore, the electric field strength is very sensitive to the angle of incidence and the depth of the scratch.

An intelligent laser machining system is developed for precision processing of superhard materials, such as diamond, silicon carbide, silicon nitride, cubic boron nitride, etc. Multiple processing functions, such as laser cutting, laser engraving, laser cleaning and polishing, can be realized by automatically adjusting laser beam parameters. The laser wavelength is 532 nm that is obtained by the second-harmonic generation of a diode-pumped solid-state laser at 1064 nm. The processing system is highly intelligent and automated, from surface scanning and measurement to self-adjustment of laser beam parameters and motion control variables during processing. In our processing, the workpiece is first scanned using a laser sensor and a 3-D profile of the workpiece is created for customer evaluation. Then, with operator’s input of processing requirements, an optimal processing procedure is designed in terms of comprehensive consideration of machining efficiency, processing duration, machine cost, surface quality, material loss, etc. Next, the material is flatten to a certain flatness by using a suitable engraving process, followed by polishing to a certain roughness, and finally cut to shaped pieces. In both the procedure design and material processing, an artificial neural network method is used in the optimization and adjustment of laser beam and motion control parameters. In the experiment of silicon carbide processing, >10-mm thick bulk materials can be cut with nearly vertical edges and polished with ~0.1 um roughness of surface. The system exhibits broad prospects in the processing applications of superhard materials.

Optical coatings prepared by ion beam deposition are dense, with good mechanical properties and environmental stability, which have a wide range of applications in high-power lasers such as ultrafast lasers and space lasers. In the field of nanosecond-laser damage, the size, composition, density and distribution of defects in materials are closely related to laser damage. In this work, the types of defects in ion beam sputtered coatings and their effect on laser damage are investigated. Micron-scale defects and damage morphology on the surface of ion beam sputtered coatings are observed using focused ion beam scanning electron microscopy. The defects on the coatings surface are found to be mainly due to structural defects from the substrate surface and nodules formed during the coating process. Micron-scale defects have a greater impact on laser damage in coatings with stronger standing wave fields. Experimentally pits defects copied from substrates can reduce the damage threshold of high-reflective coatings by nearly a factor of two, and nodules can cause a greater laser damage threshold drop. This study helps to improve the laser damage threshold of ion beam sputtered coatings.